Mineral materials have been used for many years as thermal insulation. The mineral bodies have been formed in the shape of flat slabs or rounded pieces for insulation of walls, pipes, tanks and many other industrial and commercial devices. Such mineral thermal insulation articles have typically been composed of perlite, synthetic calcium silicates and calcium silicate hydrates, synthetic magnesium silicates and magnesium silicate hydrates, magnesium carbonate and the like.
For many years such articles were commonly reinforced by incorporation of quantities of asbestos fiber. Typical examples are described in U.S. Pat. Nos. 2,016,039; 2,033,106; 2,062,879; 2,247,355; 2,326,516 and 2,326,517; 2,602,754; 3,257,220; 3,449,141. In more recent years, however, asbestos has been removed from the insulation products and the latter have been reinforced by materials such as glass fiber. Typical of the asbestos-free articles are those described in U.S. Pat. Nos. 3,501,324; 3,679,446; 3,965,020 and 4,162,924.
Because of their essentially mineral nature, all of these insulation articles have quite long service lives, commonly measured in years. If, for instance, a cylindrical mineral insulation is placed on a high temperature pipe in a manufacturing plant it can be expected that that insulation article will normally remain in position for a number of years and will be removed only if accidentally damaged or if there is reason to need access to the underlying pipe, as for repair, replacement or relocation of the pipe. In a large manufacturing plant, oil refinery, or the like it will therefore be expected that there will be large numbers of mineral insulation articles throughout the facility and that those insulation articles will be of different ages and types with older asbestos-containing materials still in use with or in proximity to newer asbestos-free materials.
Because of the current governmental regulations which require special precautions to be taken when workers handle asbestos-containing products, it is important to the insulation user to be able to identify which of the insulations contain asbestos and which do not. In the past, two different types of identification procedures have been used, but both have serious shortcomings. The first method involves taking a sample of the insulation article in question and performing a petrographic analysis on it to identify the presence of asbestos fiber in the non-asbestos mineral matrix. This is a costly and very time consuming process, particularly when a large number of pieces of insulation must be examined. In addition, many smaller manufacturing companies and the like which use mineral insulation have neither the facilities nor the personnel to perform such analysis. The second procedure has been to apply to the surface of the insulation articles some sort of visual identifying indicia. Commonly this has been in the form of a stripe of colored paint applied to the outer surface of each piece of insulation. While this can be done quickly and economically as part of the insulation manufacturing process, the paint stripe so applied frequently degrades and disappears in the high temperature service environment of the insulation. Thus when workers several months or years later are faced with handling the insulation, there is no longer any visual means associated with the piece of insulation by which they can determine whether or not it contains asbestos. Since in the absence of any direct identification of a material as being asbestos-free, governmental regulations require that it be handled as though it contained asbestos, the insulation customer must therefore use the expensive precautions associated with asbestos fiber containing materials or submit the installation articles for the expensive petrographic analysis to establish the absence of asbestos fiber.
It would therefore be of considerable advantage to have an identification system which would provide an unequivocal and permanent visual indication that the particular mineral insulation article in question was free of asbestos fiber content.